Stability and maturity of maize stalks compost as affected by aeration rate, C/N ratio and moisture

14 Pages·2015·0.76 MB·English

Journal of Soil Science and Plant Nutrition, 2015, 15 (3), 751-764
RESEARCH ARTICLE
Stability and maturity of maize stalks compost as affected
by aeration rate, C/N ratio and moisture content
W. M. Nada
Department of Soil Science, Faculty of Agriculture, Menoufia University, Shebin El-Kom 32514, Egypt.
*Corresponding author: [email protected]
Abstract
To estimate the order of importance of factors affecting the stability and maturation of compost, cow feces
and maize stalks were co-composted at different aeration rates “AR” (22, 44 and 66 L kg-1 DM . min-1) of C/N
ratios (16, 19, 22), and moisture contents “MC” (60 %, 65 %, 70 %). A composting process was monitored by
physical and chemical methods. The thermophilic phase with all treatments was long enough to meet sanitation
requirements. The emitted carbon dioxide and the losses total organic carbon and total extractable carbon
increased with increasing aeration rate, there was a significant difference between the treatments with low and
high aeration rate, but no significant differences between those two treatments and the moderate aeration rate.
The total nitrogen contents of all treatments decreased during the thermophilic phase, while it was increased after
that for all treatments except T8. The compost with the highest initial C/N ratio was significantly different from
the other treatments and had the highest values of humic substances, degree of humification and humification
rate. The compost with the lowest initial C/N ratio was significantly different from the other treatments and had
the lowest germination index (57–67%). Aeration rate was the main factor influencing compost stability, while
the C/N ratio mainly contributed to compost maturity, and the moisture content had an insignificant effect on the
compost quality. The recommended parameters for composting are an aeration rate of 0.44 L kg-1 DM. min-1 and
a carbon to nitrogen ratio of 19 with moisture content of 60–70%.
Keywords: Composting, agricultural waste, compost, quality, stability, maturity
1. Introduction pathogen content. Manure composting involves the
breakdown of complex and simple organic materials
The amount of cow waste generated in Egypt has by aerobic microorganisms (Novinscak et al, 2007).
increased dramatically with the rapid development On the other hand, agricultural wastes in Egypt are
of cow farms. These wastes can cause hygiene considered a big problem facing farmers and officials.
hazards, odor pollution, and ground and surface The amount of these wastes is about 14 million
water pollution from the leaching of pollutants, tons annually. These amounts of crop residues are
if not properly treated. Also, increased use of burnt in several governorates. It is environmentally
animal waste has brought hygienic aspects into undesirable and is practiced by farmer. Average crop
focus, particularly the need to significantly reduce residues of maize stalk in Egypt are 4.1 million tons
751
752 Nada
(Badawi and Tantawi, 2004). Bulking agents are (Gao et al, 2010), while maturity refers to the amount
always required to modify the properties of animal of degradation of phytotoxic organic substances and
manure during composting because of the high is generally measured by the germination index or
moisture contents, low C/N ratio and high density of plant bioassays (Said-Pullicino et al, 2007). However
animal manure. The maize straw is rich in carbon and none of these methods give an absolute parameter.
has a low density and low moisture content, making it Compost is a very heterogeneous biomass and the
suitable for use as a bulking agent during composting different chemical methods exploited to determine
(Kumar et al, 2010). maturity level are only suitable for certain families
As an agricultural country, Egypt needs large amounts of materials. Govi et al. (1993) reported a poor
of organic fertilizers to improve crop yields and correlation between the degree of humification (DH),
quality, and maintain or increase the nutrient status compost protein and hemicelluloses rich materials
of soil and improve its structure. Fresh cow feces are due to the formation of humic-like molecules. While
a valuable resource for organic fertilizers because Marco et al. (2004) found a high correlation between
of their high organic matter and nutrient content. humification parameters and water-soluble carbon
However, fresh cow waste is unsuitable for direct land (WSC) that is possible to monitor the composting
application because of the unstable organic matter, maturation process more easily and rapidly avoiding
pathogens, weed seeds and the difficulties associated longer and more expensive analytical procedures.
with preservation and transportation. Composting is The aeration rate (AR) is considered to be the most
an effective and economical method for the treatment important factor influencing successful composting
of animal manure prior to land application, in which (Diaz et al, 2002). Insufficient aeration can lead to
pathogens and weed seeds are destroyed and the anaerobic conditions due to the lack of oxygen, while
highly heterogeneous solid state organic matter excessive aeration can increase costs and slow down
is transformed to more stable and mature humic the composting process via heat, water and ammonia
substance by the activity of bacteria, epiphytes and losses. The optimal AR depends on the composition
actinomycetes (Badawi and Tantawi, 2004). Also, of the raw materials and ventilation methods (Bernal
stable and mature compost can be applied to soil as et al, 2009; Shen et al, 2011).
an organic amendment to improve plant growth and The initial carbon to nitrogen (C/N) ratio is one of the
soil fertility, as well as enhancing the function of soil most important factors influencing compost quality.
for carbon sequestration. However, the application of In general, initial C/N ratios of 25–30 are considered
unstable and immature compost would fix nitrogen ideal for composting (Kumar et al, 2010). However,
in the soil and restrict plant growth by competing recently some researchers have successfully carried
for oxygen in the rhizosphere and releasing toxic out composting at lower initial C/N ratios (Ogunwande
substances (Bernal et al, 2009). et al, 2008). Composting at lower initial C/N ratios
The stability and maturity of compost are often can increase the amount of manure treated, but can
referred to as the compost quality. The stability also increase the loss of nitrogen as ammonia gas.
typically refers to microbial activity and can be During composting, the moisture content (MC) is
defined by the emitted carbon dioxide, the heat important for transporting the dissolved nutrients
released, respiration index or the conversion of required for the physiological and metabolic activities
various chemical species in compost organic matter of microorganisms. The optimum MC depends on the
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Stability and maturity of maize stalks compost as affected by aeration rate... 753
specific physicochemical properties and biological 2. Materials and Methods
features of the materials being composted (Liang et
al, 2003). 2.1. Feedstocks composition
The interaction of these factors on composting has
recently been studied by some researchers. The This study was carried out at the beginning of March
optimum MC was 60% during the composting 2013 in greenhouse of the Experimental Farm, Faculty
of green waste and food waste at a low C/N ratio of Agriculture, Menoufia University, Shebin El-Kom,
(19.6) (Kumar et al, 2010), while and the optimum Egypt. Cow feces were taken from a cow farm located
conditions for the composting of poultry manure with in Faculty of Agriculture, Menoufia University. The
wheat straw were an initial MC of 70% and an AR of feces were collected on three consecutive days before
0.54 L min-1 kg-1 OM (Petric and Selimbašic, 2008). the trial started. Maize stalks were obtained from
Although several researchers have studied the effects a research station at the Faculty of Agricultural,
of AR, C/N ratio and MC on the quality of compost, Menoufia University. The maize stalks were passed
they have focused on one or two influential factors, through a cutting mill by using threshing machine to
with few studies designed to address the interaction generate pieces ranging from 1 to 5 cm. The moisture
and order of preference for different factors impacting content (MC), total organic carbon (TOC), total
the composting process. Therefore, an orthogonal test nitrogen (TN), C/N ratio and total extractable carbon
was used to investigate the main factors affecting the (TEC) of the feed stocks were determined before
stability and maturity of composted cow manure and mixing to determine nitrogen ratios to be applied. The
maize stalks; AR (0.22, 0.44 and 0.66 L kg-1 DM min- properties of compost raw materials were carried out
1, DM: dry matter); C/N ratio (16, 19 and 22) and MC according to Page et al. (1982) and the obtained data
(60%, 65% and 70%). are shown in Table 1.
Table 1. Some properties of cow feces and maize stalks.
Moisture TOC TN C/N TEC
Materials
content (%)a (gkg-1)b (gkg-1)b (-) (gkg-1)b
Cow feces 70.52 (1.5)c 353 (5.82) 26.50 (0.06) 13.32 180.5 (6.63)
Maize stalks 8.33 (0.01) 425 (8.30) 10.30 (0.12) 41.26 209.7 (7.42)
a Wet weight basis, b Dry weight basis, C Values in parentheses are standard errors (n = 3)
2.2. Experimental set-up and design and removing compost. On the lid, there were holes
for inserting a temperature sensor and to connect the
The composting reactors were 45 L plastic cylinders carbon dioxide trapping solution. The temperature
(57 cm high and 32 cm inner diameter) (Fig., 1). sensor was connected to a temperature data logger
The vessels were consisted of two layers of plastic (HI143 T-Logger) to auto-record the data. At the
intermediated with a layer of glass wool to minimize bottom of the reactors, a 3 mm plastic grid was
heat loss. A removable plastic lid was fitted to the top installed to support the composting bed and insure
of each vessel to facilitate filling with feed stocks uniform gas distribution. There were two holes in the
Journal of Soil Science and Plant Nutrition, 2015, 15 (3), 751-764
754 Nada
bottom of the reactor for aeration (using a controllable vessels by 7.0 kg/ton of each vessel as amendment.
aquarium pump) and leachate drainage. The ARs were 0.22, 0.44, and 0.66 L kg-1 DM min-
This study was established as an orthogonal array 1. Air is entered through the compost mixture by
test L (34) lasting 60 days (Table, 2). Cow feces and aquarium pump. The aeration of all treatments was
9
the chopped maize stalks were mixed manually in intermittent with 25 min of aeration followed by 5
different amounts to adjust the C/N ratios at 16, 19 min without aeration over the whole composting
or 22, and the initial MC values to 60%, 65% or 70%. period (60 days). The compost vessels were turned on
Super phosphate (15.5 % PO) was mixed with all days 3, 7, 15, 30 and 45.
2 5

Temperature
Data logger
1M NaOH
Temperature
sensor
Cow feces and
Solid
maize stalks
sampling port
Aquarium
pump
Leachate outlet

Figure 1. Schematic Diagram of the composting vessel.
Table 2. Design of experiment
Moisture content Aeration ratea C/N ratio
Treatments
(%) (L kg-1 DM min-1) (-)
T1 60 0.22 16
T2 60 0.44 19
T3 60 0.66 22
T4 65 0.22 19
T5 65 0.44 22
T6 65 0.66 16
T7 70 0.22 22
T8 70 0.44 16
T9 70 0.66 19
a Aeration for 25 min, no aeration for 5 min
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Stability and maturity of maize stalks compost as affected by aeration rate... 755
Table 3. Total organic carbon (TOC) and total nitrogen (TN) mass balance at the end of composting
1 followed by 5 min without aeration over the whole composting period (60 days). The compost
Total organic carbon (TOC) Total nitrogen (TN)
2 vessels were turned on days 3, 7, 15, 30 and 45.
Treatment
I3nitial 2.3.SampFlein aclollection∆ aTnOdC aanalyticIanli tmiale thods Final ∆ TNb
(g kg-1 DM) (g kg-1 DM) (%) (g kg-1 DM) (g kg-1 DM) (%)
4 Solid samples (about 200 g) were taken at the beginning, after each turning and end of
T1 369 315 44 23 27 22
5 composting. Five grams of each sample were taken for MC determination by drying at 105oC
T2 382 310 51 20 27 28
T3 6398 to a consta3n4t5 weight. Th5e4 remainder 1s8a mple was div2i6d ed intotw3o2 parts. The firstpart stored at
T4 7384 4oCand t3h3e5 s econd par4t2 w asair-drie2d0 and grounde2d5 to pass thr2o3u gh a 2 mm sieve. The dried
T5 404 361 56 18 28 29
8 and ground samples were analyzed in triplicate for total nitrogen (TN), total organic carbon
T6 372 301 51 23 24 45
T7 9406 (TOC) and3 6t0o tal extract4a7b le carbon (1T8E C), humic-l2i6k e acid frac1ti9o n (HA) and fulvic-like acid
T8 10375 fraction (F3A34) . TOC was3 6d etermined 2b3y the Walkle1y9- Black Met4h0o d; TN, by indophenols-blue
T9 385 332 50 20 25 36
11 method after the Kjeldahl digestion (Pageet al, 1982).
a Based on initial carbon content, b Based on initial nitrogen content
12 Humic-like substances were extracted from the compost samples as described by Ciavatta et
13 al. (1990) and the total extractable carbon (TEC) determined by wet dichromate oxidation.
2.3. Sample collection and analytical methods fraction was determined. Degree of humification (DH
14 The extracts were fractionated into humic acids (HA) and fulvic acids (FA). After
%) was calculated by using the following equation
Solid samples (abou1t 5200 pgu) riwfiecrae titoank,e nth ea tc athrbe on co(Enqteunatti oonf 1e)a. ch fraction was determined. Degree of humification (DH
beginning, after each t1u6rning %an)d wenads ocfa clcoumlpaotestdin bgy. using the following equation (Equation1).
Five grams of each sample were taken for MC
17 (Eq. 1)
determination by drying at 105 oC to a constant
weight. The remainde1r 8samplCe awrbaso ndi vdidieodx iidnteo tpwroo duced by the compost is trapped by sodium hydroxide as sodium
parts. The first part stored at 4 oC and the second part Carbon dioxide produced by the compost is trapped
19 carbonate (Thompsonet al, 2001). As shown in Figure1, the carbon dioxide was trapped in a
was air-dried and grounded to pass through a 2 mm by sodium hydroxide as sodium carbonate (Thomp-
20 sodium hydroxide (1M NaOH) wash bottle (1 L) and then measured daily by titration with
sieve. The dried and ground samples were analyzed in son et al, 2001). As shown in Figure 1, the carbon di-
triplicate for total nitro2g1en (T1NM), toHtaCl lo troga an ipc hcearnboolnp hthaolexiind ee wndasp torainppt,e ad fitne ar saodddiuinmg h eyxdcroexsisd e1 M(1M B NaCaOlH.)
2
(TOC) and total extractable carbon (TEC), humic-like wash bottle (1 L) and then measured daily by titra-
22 A water extract was prepared for the determination of the seed germination index (GI). Fresh
acid fraction (HA) and fulvic-like acid fraction (FA). tion with 1M HCl to a phenolphthalein endpoint, after
23 compost samples taken at mixed with deionized water at a 1:10 ratio (mass ratio) and shaken
TOC was determined by the Walkley-Black Method; adding excess 1M BaCl.
2
TN, by indophenols-b2lu4e meftohor d1 a fhte, rt htheen Kcjeelndtarhifl ugedA a tw a4t0er0 0ex rtrpamct wfoars 2pr0e pmariend afonrd t hfeil tdeerteedrm tihnarotioung h 0.45 µm membrane
digestion (Page et al, 129582). filters. The GI was determofi ntheed siene dtr igpelrimcainteatiuosni ningd teexn ( GtoIm). aFtroe sshe ecdoms p(Losytc opersicon esculentum
Humic-like substances were extracted from the samples taken at mixed with deionized water at a 1:10
26 L.) and a water extract. Eight millilitre of the water extract was pipetted into Petri dishes (10
compost samples as described by Ciavatta et al. (1990) ratio (mass ratio) and shaken for 1 h, then centrifuged
27 cm in diameter) packed with a piece of filter paper. Ten seeds were evenly scattered on the
and the total extractable carbon (TEC) determined at 4000 rpm for 20 min and filtered through 0.45 µm
by wet dichromate o2x8idatiofnil.t eTr hpea peexrtr aacntsd iwnecrue batedm aemt b2r0a n±e fi1l toeCrs . fTohre 4G8I wh aisn d ethteerm dianrekd. i nD teriipolinciaztee d water was used as a
fractionated into humic acids (HA) and fulvic acids using ten tomato seeds (Lycopersicon esculentum
29 control. The GI was calculated byusing the follows equation (Equation 2)(Rui et al, 2012).
(FA). After purification, the carbon content of each L.) and a water extract. Eight millilitre of the water
30 (Eq. 2)
31 Journal of Soil Science and Plant Nutrition, 2015, 15 (3), 751-764
32
5
756 Nada
extract was pipetted into Petri dishes (10 cm in di- remained above 60 oC for the longest time. This dif-
ameter) packed with a piece of filter paper. Ten seeds ference is because the lowest AR leads to a lower or-
were evenly scattered on the filter paper and incubat- ganic degradation rate and lower losses of moisture
ed at 20 ± 1 oC for 48 h in the dark. Deionized water and heat. The thermophilic phase (>55 oC) for all
was used as a control. The GI was calculated by using treatments lasted longer than 7 d. After the easily de-
the follows equation (Equation 2) (Rui et al, 2012). gradable compounds were depleted, the composting
entered the curing phase and the temperature slowly
dropped (Shen et al, 2011). The statistical analysis
showed that, the AR had a significant influence on the
2.4. Statistical analysis change in temperature (p = 0.021), but the MC and
the C/N ratio did not significantly affect the tempera-
Data were analyzed by a one-way analysis of variance ture (p = 0.611, p = 0.133). The CO–C concentra-
2
(ANOVA); the LSD-t test was used for significant dif- tions in the outlet air during composting (Figure 2)
ference testing. Pearson’s correlation coefficient was were significantly correlated to their temperatures
used for the analysis of bivariate correlations. The (R = 0.350–0.941, p = 0.010–0.024). Carbon diox-
SPSS 11.5 software for Windows was used for all sta- ide was mainly emitted during the thermophilic pe-
tistical analyzes (SPSS Inc., 2002). riod because of the degradation of easily degradable
carbon under vigorous bacterial and fungal activity.
3. Results and Discussion During the curing period, CO emissions are related
2
to the degradation of complex organic molecules such
3.1. Temperature and carbon dioxide as lignin and lignocelluloses by some fungi and ac-
tinomycetes (Kumar et al, 2010). After composting,
Figure 2 shows the changes in the ambient tempera- the CO emissions from T1 to T9 were 180–470 g
2
ture and composting temperature. The ambient tem- CO–C kg-1 of initial total carbon. Treatment T8 had
2
perature ranged from 20 oC to 30 oC. The composting the lowest CO emissions indicating that a high MC
2
materials went through the three typical degradation and a low C/N ratio restricted organic degradation
phases: mesophilic, thermophilic and curing. Increase even at a high AR. This low degradation rate occurred
temperature at the beginning may be due to high because the large pieces of waste material (diameter
available carbon content which it provides a favour- 3 cm) combined with a low C/N ratio and high MC
able condition for the growth and biological activ- reduced the oxygen diffusion rate into the interior of
ity of microorganisms (Novinscak et al, 2007). The the waste particles, reducing microbial activity (Shen
temperature tends to decrease after the thermophilic et al, 2011; Rui et al, 2012). Also, the statistical analy-
phase due to the loss of substrate and a decrease in mi- sis showed that neither the AR, C/N ratio nor the MC
crobial activity (Ogunwande et al, 2008). Because of had a significant influence on CO emissions. Wang
2
the metabolism of the psychrophilic and mesophilic et al. (2004) suggested that, the composts from cattle
microbes, the temperatures of treatments with mod- and pig manure were more stable when the respira-
erate and high ARs reached the thermophilic phase tion rates were below 1 mg CO–C g-1 DM d-1. Higher
2
(>55 oC) within the first 1–7 d. The temperatures of CO emissions indicate unstable compost that needs
2
the treatments with the low AR rose more slowly but further decomposition. On day 40, the CO emissions
2
Journal of Soil Science and Plant Nutrition, 2015, 15 (3), 751-764
Stability and maturity of maize stalks compost as affected by aeration rate... 757
from treatments T1, T3, T5, T8 and T9 were 0.60– d-1. The low CO emission rate for treatment T8 was
2
0.90 mg CO–C g-1 DM d-1, but the emissions for the related to its low activity.
2
other treatments were 1.30–2.50 mg CO–C g-1 DM
2
80 35
AR =0.22 L.kg -1DM.min-1 AR =0.22 L.kg -1DM.min-1
70 30
oTemperature (C)34560000 aTTTm147binet -1-1CO-C (g.kgDM.d)211220505 TTT147
20 5
10 0
0 10 20 30 40 50 60 0 10 20 30 40 50 60
Time (days) Time (days)
80 35
AR =0.44 L.kg -1DM.min-1 AR =0.44 L.kg -1DM.min-1
70 ambinet 30
oature (C)5600 TTT258 -1-1kgDM.d)2205 TTT258
mper40 C (g.15
Te30 O-210
C
20 5
10 0
0 10 20 30 40 50 60 0 10 20 30 40 50 60
Time (days) Time (days)
80 35
AR =0.66 L.kg -1DM.min-1 AR =0.66 L.kg -1DM.min-1
70 30
omperature (C)456000 aTTTm369binet -1-1C (g.kgDM.d)122505 TTT369
Te30 CO-210
20 5
10 0
0 10 20 30 40 50 60 0 10 20 30 40 50 60
Time (days) Time (days)
Figure 2. Temperature of the compost in the vessel and CO content in the outlet air during composting (AR: aeration rate).
2
Journal of Soil Science and Plant Nutrition, 2015, 15 (3), 751-764
758 Nada
3.2. Total organic carbon and total nitrogen after day 30, which is related to the minor losses of
NH by aeration coupled with the low carbon and va-
3
The total organic carbon (TOC) contents of all treat- pour emissions due to the inactive state of the material.
ments decreased during composting ( is shown in At the end of composting, the TN losses were 19% to
Figure 3). As with the CO emissions, the rates of 45% (Table 3). The statistical analysis showed that AR
2
decrease were greater during the thermophilic phase (p = 0.041) had the most significant influence on the
(60–95% of the total carbon loss) and less during the nitrogen losses compared with the MC (p = 0.725) and
curing phase. Decreasing TOC content during com- C/N ratio (p = 0.437). There was a significant differ-
posting process could be related to the mineraliza- ence between the treatments with low and high ARs (p
tion of the organic matter by microorganisms. A total = 0.016), but no significant differences between those
of 36–56% of the initial TOC (369–406 g kg-1 DM) two treatments and the moderate AR (p = 0.472, p =
was lost at the end of composting (Table 3). Higher 0.342). Thus, we conclude that higher ARs can cause
TOC losses occurred with the higher AR except for higher nitrogen losses.
treatment T8, which had low activity. At the end of
composting, CO was the main source of carbon loss, 3.3. Humic substances and humification parameters
2
accounting for 70–85% of the total carbon losses. The
remaining carbon losses were caused by the emission The total extractable organic carbon (TEC) and humified
of CH and other volatile organic compounds (such as humic-like substances (HA + FA) content is detailed in
4
methyl mercaptan and dimethyl sulphide) (Hanajima Figure 4. This figure shows that TEC of the compost dis-
et al, 2010). The statistical analysis showed that AR (p played a similar trend to TOC, which decreased rapidly
= 0.032) had the most significant influence on the de- at the first 15 days after composting process initiation.
creasing of TOC compared with the MC (p = 0.71) and It was followed by a gradual decrease to below after 45
C/N ratio (p = 0.42). There was a significant difference days until the end of incubation period (60 days). The
between the treatments with low and high ARs (p = analytical results in Figure 4 show that, the TEC level de-
0.012), but no significant differences between those creased from 184 to 147 g/kg in T1, from 192 to 155 g/
two treatments and the moderate AR (p = 0.075, p = kg in T2, from 199 to 172 in T3, from 192 to 163 g/kg in
0.033). Thus, the obtained data conclude that higher T4, from 202 to 180 g/kg in T5, from 180 to 143 in T6,
ARs can cause higher organic carbon losses. These re- from 203 to 180 g/kg in T7, from 185 to 167 g/kg in T8
sults are in agreement with those obtained by Rui et and from 190 to 160 g/kg in T9 treatment. The highest de-
al. (2012). Figure 3 shows the variation in the TN con- creasing rate of TEC appeared in T6 (66 L.kg-1 Dm.min-1
tent. The TN contents of treatments with moderate and AR, 16 C/N and 65% MC), while the lowest one noticed
high ARs decreased during the thermophilic phase be- in T8 characterized by 0.44 L.kg-1 Dm.min-1, 16 C/N and
cause of intensive NH volatilization, but only minor 70% MC. The statistical analysis showed that AR (p =
3
changes in TN were observed for treatments at the low 0.021) and C/N ratio (p = 0.035) had the most significant
AR. The TN increased after the thermophilic phase for influence on the TEC losses compared with the MC (p
all treatments except T8, because the rate of N loss as = 0.725). There was a significant difference between the
NH was slower than, the rate of dry matter loss as CO treatments with low and high ARs (p = 0.016), but no
3 2
and water evaporation (Huang et al, 2006). The TN in significant differences between those two treatments and
treatment T8 decreased slightly, but had little variation the moderate AR (p = 0.714, p = 0.342). Also, high sig-
Journal of Soil Science and Plant Nutrition, 2015, 15 (3), 751-764
Stability and maturity of maize stalks compost as affected by aeration rate... 759
nificant difference was occurred between the treatments T5 (65% moist) and T7 (70% moist) MC (p = 0.032, p =
with low and high C/N (p = 0.013), and no significant dif- 0.022), but no significant differences between T3 and T5
ferences between those two treatments and the moderate MC (P = 0.633). Continuously, the degree of humifica-
C/N (p = 0.632, p = 0.542). Thus, we conclude that higher tion (DH, %) of compost samples is illustrated in Figure
ARs and low C/N ratio can accelerate the degradation of 5, which it was increased with increasing time (except
organic carbon, and consequently cause higher TEC loss- T8). Composts T8 showed a low maturation level , since
es. As reported by Ciavatta et al. (1990) and Marco et al. DH% was 58.6; composts T2, T3, T5, T6 and T9 resulted
(2004), different studied treatments confirmed that TEC to have reached a high maturation level (DH% > 70),
decreased predominantly during composting due to the while composts T1, T4 and T7 showed intermediate val-
intense mineralization process. TEC fraction included all ues of DH% (68.0, 65.0 and 63.3 respectively), indicating
the easily mineralizable organic fractions and other more an incomplete stabilization of this composts. Throughout
humified and hence more biodegradation resistant frac- composting, the highest values of DH% accompanied the
tions (Huang et al, 2006). The content of humic acid-like highest C/N ratio treatments (T3, T5, T7) and/or the mod-
substances (HA + FA) in the composts increased during erate C/N ratio (T2, T4, T9), while the lowest C/N ratio
the first phase (15 days), which it were decreased slightly treatments (T1, T6, T8) comes later. Also, high DH val-
after that until the end of incubation period (Figure 4). ues observed for the treatments that have the highest aera-
This increasing in the first phase could be due to either the tion rate (0.66 L.kg-1 DM.min-1), while the lowest one re-
formation of humic acid-like substances or the separation corded to the lowest aeration rate (0.22 L.kg-1 DM.min-1).
of these substances from other more complex carbon However, the treatments treated with moderate moisture
compounds (Huang et al, 2006). While decreasing rate (65%) gave the highest values of DH compared with the
in the latter phase may be related to high amount of in- other two moisture rates (60% and 70%).
soluble compounds (Figure 4). Throughout composting,
the highest values of humic-like substances (HA+FA) 3.4. Germination index (GI)
accompanied the highest C/N ratio treatments (T3, T5,
T7), followed by moderate C/N ratio (T2, T4, T9) and The GI is a sensitive indicator of maturity and phytotoxic-
finally C/N ratio (T1, T6, T8) treatments. The statisti- ity (Rui et al, 2012). Figure 6 shows the changes in GI for
cal analysis showed that C/N ratio (p = 0.041) had the all treatments. The GIs of all treatments decreased slowly
most significant influence on the humic-like substances during the early phase. This drop may be attributed to the
(HA+FA) variations compared with the ARs (p = 0.625) production of low molecular weight short chain volatile
and MC (p = 0.537). Also, the compost with the highest fatty acids (primarily acetic acid) and the release of toxic
initial C/N ratio was significantly (P = 0.021) different concentration of ammonia (Fang et al, 1999). The GIs
from the other treatments and had the highest values of increased with the decomposition of these toxic materi-
humic-like substances. There is no significant differ- als. The statistical analysis showed that the C/N ratio had
ence between the treatments with low and high ARs (p = a significant influence on GI (P = 0.005), but MC (P =
0.651) and between those two treatments and the moder- 0.762) and AR (P = 0.864) were not important influential
ate ARs (p = 0.802, p = 0.402). Likewise, there are no factors. No significant differences were found between
significant differences between the treatments under dif- the treatments with C/N ratios of 19 and 22 (P = 0.331),
ferent moisture levels. However, high significant differ- but both of those were significantly different from the
ences were observed between either T3 (60% moist) or treatments with a C/N ratio of 16 (P = 0.003, P = 0.005).
Journal of Soil Science and Plant Nutrition, 2015, 15 (3), 751-764
760 Nada
A GI of more than 80% indicates phytotoxic-free and ma- 57–67%, suggesting that a longer time was required to
ture compost (Rui et al, 2012). At the end of composting form mature compost when a low C/N ratio was used.
(60 days), the GIs for treatments with a C/N ratio of 22 This result is similar to that found by Huang et al. (2006),
(T3, T5, T7) were higher than treatments with a C/N ratio who used two static aerobic piles (initial C/N ratios of 15
of 19 (T2, T4, T9) at the same AR, except the lowest aera- and 30) to compost pig manure, and found that at day 63,
tion rate where the treatment with C/N ratio of 19 was the GIs were 46% and 85% for C/N ratios of 15 and 30,
higher than the treatment with a 22 C/N ratio. While both respectively. The GIs of all treatments with moderate and
the treatments with C/N ratios of 19 and 22 were much high C/N ratios except T7 exceeded 80%. The high MC
higher than treatments with a C/N ratio of 16. The GIs of (70%) and low AR (0.22 L kg-1 DM min-1) in treatment
the treatments at the lowest C/N ratio (T1, T6, T8) were T7 restricted the decomposition of toxic compounds.
450 30
AR =00.22 L.kg -1DMM.min-1 AAR =0.22 L.kgg-1DM.min-1
400 25
M) M)
D D
-1TOC (g.kg350 -1TN (g.kg20
300 15
TT1 T4 T7 T1 T4 T7
250 10
0 3 7 15 300 45 60 0 3 7 15 30 445 60
Time (days) Timee (days)
4500 30
ARR =0.44 L.kg -1DDM.min-1 AAR =0.44 L.kgg-1DM.min-1
4000 25
M) M)
D D
-1OC (g.kg 3500 -1TN (g.kg20
T
3000 15
TT2 T5 T8 T2 T5 T8
2500 10
0 3 7 15 30 45 60 0 3 7 15 30 445 60
Time (days) Timee (days)
450 30
AAR =0.66 L.kg -1DM.min-1 AR =0.66 L.kg -1DM.minn-1
400 25
M)
-1TOC(g.kgD 350 -1N (g.kgDM)20
300 T15
T3 T6 T9 T3 T6 T9
250 10
0 3 7 15 30 45 60 0 3 7 15 30 445 60
Time (days)) Time (days)
Figure 3. Total organic  carbon (TOC) and total nitrogen (TN) during composting (AR: aeration rate).Values are means ±
standard error (n = 3).
Journal of Soil Science and Plant Nutrition, 2015, 15 (3), 751-764